The population, particularly those engaged in industry and other occupations, is exposed to an ever increasing number of contact allergenic simple chemical compounds. At the same time a large body of data has accumulated which shows that, under appropriate circumstances, it may be possible to induce specific immunologic tolerance for cell- mediated contact sensitivity to simple chemicals. In guinea pigs this can be done by injecting or feeding the chemical prior to the first exposure by contact. Thus it may be possible to prevent the development of contact sensitizaton in industry and other occupations, where exposure to certain potent contact allergens can be anticipated. The broad objective of the proposed project is to develop a method for induction of specific immunologic tolerance against strongly immunogenic contact allergens by feeding or injecting structurally related but non- immunogenic chemical and presumably unconjugated, simple chemicals as tolerogens. This would permit the induction of tolerance without exposing individuals to the possible harmful immunologic (or toxicologic) properties of the strongly immunogenic chemicals. The proposed experiments will be carried out in guinea pigs, using 2,4 dinitro-1-chlorobenzene as the strongly immunogenic chemical and 1,2, dichloro-4-nitrobenzene,1,4 dichloro-2-nitrobenzene and other non- immunogenic chemicals as tolerogens. Attempts will be made also to apply the same principle to specific hyposensitization and desensitization to simple chemical contact allergens in guinea pigs.